1. Technical Field
The present invention relates to a production method of spherical oxide powder and a production apparatus of spherical powder, and a composite dielectric material suitable for use in the high frequency region, a substrate and a production method of the substrate.
2. Background Art
A fine oxide powder can be obtained by mixing materials, drying the mixture obtained and subsequently calcinating the dried mixture, and then pulverizing the calcinated mixture with a pulverizing machine such as a ball mill, or the like.
Such oxide powders are used as powders of single material for the cases of dielectric materials and magnetic materials, and some other times used as pastes mixed with an organic vehicle and as composite materials combined with a resin material. An oxide powder which is used as a paste or a composite material is required to have dispersion properties and packing properties for an organic vehicle and a resin material (hereinafter, a generic term “a resin material” will be used) Here, the dispersion properties mean the degree of dispersion of an oxide powder in a resin material, and it is preferable that an oxide powder is dispersed in a resin material with a higher degree of uniformity. In addition, the packing properties signify the quantity of an oxide powder filling in a resin material, and it is preferable that a larger quantity of an oxide powder fills in a resin material. A factor for an oxide powder to acquire the dispersion properties and packing properties for resin materials is the particle size of the powder. In addition to the above described method, a precipitation method can produce oxide powders in which method oxide powders are produced from the liquid phase, but the particle size of the oxide powders thus produced is too fine to acquire the dispersion properties and packing properties for resin materials. On the other hand, an oxide powder obtained by pulverizing as mentioned above, and accordingly the particle shape is so irregular that the dispersion properties and packing properties for resin materials cannot be acquired. In other words, another factor for an oxide powder to acquire the dispersion properties and packing properties for resin materials is the particle shape. Incidentally, in the present specification, a powder signifies an ensemble of particles; when the substance concerned is judged to be appropriately referred to as a powder as being an ensemble of particles, the substance will be referred to as “powder”, and when the substance concerned is judged to be appropriately referred to as particles as being units constituting a powder, the substance will be referred to as “particles.” Since the powder and the particle share the common fundamental unit, needles to say there are sometimes no substantial differences between the powder and the particle. Accordingly, there are some cases where either the expression of “powder” or the expression of “particles” can be used.
For the purpose of acquiring the dispersion properties and packing properties for resin material, the particles constituting a powder are preferably spherical, and more preferably nearly of the true sphere. In addition, it is preferable that the particle size is uniform, that is, the width of the particle size distribution is small.
A variety of production methods of spherical oxide powders have hitherto been proposed, for example, as in Japanese Patent Laid-Open No. 2000-107585, Japanese Patent Laid-Open No. 8-48560, and Japanese Patent Laid-Open No. 5-105502.
Japanese Patent Laid-Open No. 2000-107585 discloses a production method of spherical oxide powder in which a slurry is prepared by kneading an oxide powder with an appropriate binder, and the slurry is dripped on a high temperature heating body.
In addition, Japanese Patent Laid-Open No. 8-48560 discloses a production method of fine molded oxide spheres in which the oxide powder granules obtained by the spray granulation method are used as nuclei, in producing the fine molded oxide spheres which are produced by molding the oxide powder obtained by the stirring granulation method.
Furthermore, Japanese Patent Laid-Open No. 5-105502 discloses an injection molded material which contains the oxide spherical powder having the mean particle size of 7 μm or below and a binder resin.
The above described production method of Japanese Patent Laid-Open No. 2000-107585 is, however, not suitable for the composite formation with resin materials, since the obtained powder is surely spherical, but the particle size is as large as 0.3 to 1.2 mm (300 to 1200 μm).
The method disclosed in Japanese Patent Laid-Open No. 8-48560 aims at obtaining powders having the size of 0.02 to 0.4 mm (20 to 400 μm) not suitable for composite formation with resin materials.
Japanese Patent Laid-Open No. 5-105502 discloses an injection molded material containing an oxide spherical powder having the mean particle size of 7 μm or below and a binder resin, but does not disclose any specific techniques of obtaining spherical oxide powders.
As stated above, conventionally it has been difficult to obtain those spherical oxide powders having particle size and its distribution, which are suitable for composite formation with resin materials. In particular, no technique has been found for obtaining multicomponent oxides such as a composite oxide.
As a method of obtaining spherical oxide powders other than those described above, the plasma-flame method can be considered to be used. The method using plasma flame consumes an electric power of several hundred kW in addition to the consumption of a large volume of expensive argon gas as carrier gas, and hence there is a problem that the cost is high. Accordingly, the method using plasma flame is still in a position far way from the application to mass production.
Accordingly, the present invention provides a method capable of producing, without raising the cost, an oxide powder which has the particle size suitable for composite formation with resin materials, and is excellent in the dispersion properties and packing properties for resin material. Furthermore, the subject of the present invention is to provide an apparatus suitable for use in such a method of producing a spherical oxide powder. Another subject of the present invention is to provide, by using such spherical oxide powders, a composite dielectric material having a high dielectric constant ε and a low tan δ, and being suitable for use in the high frequency GHz band, and a substrate produced by using the composite dielectric material of the present invention.